Sound reproduction



Dec. 12, 1933.

D. C. HICKSON SOUND REPRODUCTION Filed Dec. 19, 1929 2 Sheets-Sheet l FZG 5y lay $0M Patented Dec. 12, 1933 1,938,697 T F C SOUND REPRODUCTION Daniel C. Hickson, New York, N. Y., 'as signor to Electrical Research Products Inc., N. -Y., a corporation of Delaware New York,

Application December 19, 1929. Serial No. 415,256 1 5 Claims. 01. 179-4004) This invention relates to-soundreproducing systems and has for its principal object facilitating the superimposing oio'ther sounds upon the sound accompaniment of a motion picture.

In the showing of sound picturesit is frequently desired to superimpose upon the regular sound accompaniment of speech or music other sounds representing appropriate natural noises, or eflects. When the picture is not provided with a synchronized sound record a suitable accompaniment is desirable and this may be enhanced in interest by the superposition of the sounds from a plurality of records. The character of the superimposed sounds is, of course, amatter for artistic judgment.

The regular sound reproducing equipment for sound picture projection comprises two turntables for disc records and two electricalreproducers which are connected to the sound projector circuits through a fader potentiometer. Generally the turn-tables are synchronized with the picture projector, but in some cases the synchronization isdispensed with and in other cases two additional non-synchronized turn-tables are provided for incidental "music. synchronized turn-tables, are connected to the loud speakers through a fader poteniometer to permit the gradual transition from the one record to the other.

To permit the superimposing of the sounds from the two reproducers or a pair, there is provided by this invention a switching arrangement whereby either half of the fader poteniometer can be replaced by an auxiliary potentiometer having its own adjustable contact. The output leads from the auxiliary potentiometer and from" the operative half of the fader areconnected in parallel to the input of the sound projector cir-' ations of the response and in high quality systems suchvariations are compensated by the use of suitable equalizing circuits. 'It is furthermore'the usual practice to employ networks for reducing stylus scratch noise.- The proper iunctioning of these equalizers and networks depends upon the impedances of the several partsof the system remaining constant and, if this constancy is not maintained under all conditions of operation the" quality of the reproduced sound will be vitiated.

- Fig. lis a schematic of a sound reproducing .Fig. '2 when the switch is thrown to the left.

These, like the system comprising the usual arrangement of two record turn-tables from which sound can be projected one at a time; i 1

Fig. 2 illustrates schematically a circuit and switching arrangement in accordance with this invention, which enables both records to be played simultaneously; I

Fig. 3 is a simplified circuit diagram of the circuit of Fig. 2 when the'switch is in the normal position, the switch being omittedfor clearness;- 1

Fig. 4 is a simplified diagram of the circuit of Fig. 2 whenthe switch is thrown to the right;

Fig. -5 is a simplified diagram of the circuit of Fig. 1 illustrates a circuit diagram of a non-synchronized type of sound reproducing system in common use for playing an accompaniment to" motion pictures.

The system comprises two similar stylus-operatedreproducers 10 and 10 which are energized by records on turn-tables 11 andl'l respectively. one terrninal of each reproducer is connected to a common grounded output terminal 13; The; ungrounded ends of reproducers l0 and 10' are connected respectively toterminals' 1- and 3 ofa Hider-"potentiometer 14 which is grounded at its mid-point terminal 4. An adjustable contact 15, whichis brought out from the casing of the fader at terminal 2, is connected through a re sistance '16lto the ungrounded output terminal '13 of the sound projector circuit. Networks 17 and 17', each consisting of a series connected capacity, inductance and resistance, are shunted across reproducer units '10 and '10, respectively, for the purpose'of reducing stylus scratch noise. The input of a sound projector circuit comprising" an amplifier 18 and a horn 19, is connected to the terminals 13, 13 of the reproducer circuit.

The use of the scratch reducers is optional,

although they are usually employed. There are eration of the system requires fair uniformity of 1 line impedance; to maintain a fairly uniform line impedance at the various positions of the Iader arm is the function of resistance 16. v

In practice, although both reproducers are generally in operation, the output into thesound projecting circuitis obtainedifrom only one reproducer at a time,'dependi ngupon the position of the adjustable contact of the fader potentiom eter. For example, if the soundaccompaniment is being playedfrom a recordon turn-table 11-} reproducerunit 10 is energizedand theelectricpulses corresponding to" the vibrations ,of the stylus are transmitted through thatportion of the fader between" its terminals 1 and 4, and he volume of reproduced sound is controlled by the position of the movable contact 15, which of course must also be located between terminals 1 and 4. When the adjustable contact is in this position, no energy is received at terminals 13, 13' from reproducer 10 because its energy passes only through that part of the fader between terminals 3 and 4. Now, when it is desired to project the selection played by reproducer 10' instead of reproducer 10, the gradual transitionj'from the first record to the second is effected by moving the adjustable contact of the fader toward terminal 4, past it, and then on toward terminal-3 until the desired volume of sound is obtained. Since the output from only one record can be projected at a time, the system does not permit the superimposing of sound effects by the other record.

Fig. 2 illustrates a circuit and switching arrangement which includes the reproducing set of Fig. land permits the simultaneous operation of both turn-tables, whereby the output at terminals 13, 13 is'a composite in any desired proportion of the sound oscillations from both reproducers. The parts in Fig. 2 which are identical to parts in Fig. 1 are designated by the same numbers. The additional apparatus and elements which have beenadded comprises a three-position key 20, an auxiliary potentiometer 21 and resistances 22 and 23, the former resistance being in series with resistance 16, the latter in series with the adjustable contact 24 of potentiometer 21. The showing of the fader "potentiometer 14 differs somewhat from the showing in Fig. 1, there being illustrated in Fig. 2 a built-out type, that is, one in which the contact points are individually connected to the main resistance by resistances having different values at each point. This construction keeps the line impedance more uniform for the various positions of the contact arm than does the simpler form in Fig. 1. The auxiliary potentiometer 21 is likewise of the, built-out form.

The key is interposed in the circuit in such a manner that either one of the two reproducers can be connected with its respective side of the "fader" potentiometer, while at the same time, the other reproducer is connected with the auxiliary potentiometer. One of the positions of the key is a normal position which permits the auxiliary potentiometer and resistances 22 and 23 to be eliminated so that the system can be operated as though the superimposing elements were the output line, and also short circuits resistance 22- so that the resulting circuit arrangement is simply the reproducing set shown in Fig. 1. In this and in the following figures the potentiometers are shown in the simple form as in Fig. 1 for the sake of simplicity of illustration, instead of in the more complex form of Fig. 2.

If the key is moved to the right-hand position so that the contact arms 25- and, 26 are in the position shown in dotted lines while the contact arms 27 and 28 remain in the position shown in full lines, the circuit arrangement assumes the form of the simplified wiring diagram inFig. 4, In this position of the switch,'reproducer 10 is connected to itsassociated side'of the fader between terminals 1 and 4, but reproducer 10' is disconnected from the fader at terminal 3, and instead is connected to the ungrounded terminal 7 of the auxiliary potentiometer. At the same time the contact arm 24 of the auxiliary potentiometer 'is connected to output terminal 13. It is seen that in this arrangement, the fader potentiometer controls the output of reproducer 10 while the auxiliary potentiometer controls the output of reproducer 10, and also that the output circuits from the two potentiometers are connected in parallel at the output terminals 13, 13. The strength of the signals at the output terminals of the set due to the individual reproducer units can be controlled independently by means of the movable contact arms 15 and 24.

When the key is moved to the left position so that contact arms 27 and 28 assumethe positions shown in dotted lines and arms 25 and 26 remain in the normal positions shown in full lines, the resulting circuit is that shown in Fig. 5. The only difference between the circuit arrangements of Figs. 4 and 5 is that the fader and auxiliary potentiometers are interchanged with respect to the reproducers whose outputs they control. Thus the ungrounded end of reproducer 10 is connected to terminal 3 while terminal 1 is disconnected, so that the operative side of the fader is that between terminals 3 and 4. Similarly, terminal 'I of the auxiliary potentiometer is connected to the ungrounded end of reproducer 10.

When the key is in either the left or the right position so that the outputs from both repro: ducers are in parallel at the output terminals 13, 13', the resistance 22 is in series withresistance 16, which is part of the reproducing set of Fig. 1. If this resistance were not added, the impedance at the output terminalswould be appreciably lowered bythe addition of the circuit containing the auxiliary potentiometer. Since good operation of the system, as well as the operating characteristics of equalizers, including scratch reducers, depends upon the maintenance of fairly uniform line impedance, the resistance 22 is added to obtain it. Likewise, resistance 23 is inserted in circuit with the auxiliary potentiometer for the same reason that resistances 16 and 22 are used with the fader, and should ordinarily have a value equal to their sum. Since in the normal position the auxiliary potentiometer is out of circuit, the additional resistances 22 and 23 are not required, and hence are eliminated by the switch.

While the switching arrangement in Fig. 2 connectsresistance22 in circuit with the fader potentiometer in the left and right positions of the switch, it is possible, by making changes in the connections, to place resistance 22 in series with both potentiometer circuits, that is, adjacent terminal 13. A simple method of obtaining this circuit arrangement is to interchange at the switch the connections of the two conductors which extend fromthe ends of resistance 22 to the switch. This arrangement is advantageous when both potentiometers are of thesame impedance; since then resistances-16 and 23 are equal and the potentiometers are interchangeable.

The. operation of the system is the same whether the key is thrown to the right as in the case of Fig. 4, or to the left as in the case of Fig. 5. But having available these two switching positions affords a greater flexibility than,

would be obtained if there were only one of them. The reason will become apparent from played from one record and sound. eflectswill be intermittently superimposed from the other. The key should be thrown so that the master selection is controlled by the fader while the superimposing sound is controlled by the auxiliary potentiometer. Now, when it is desired to change the master selection, the key should be thrown into the normal position so that the superimposing circuit is removed from the output terminals of the set; then the superimposing record may be replaced by the record of next master selection which should then be faded in by moving the fader contact arm 15 to the side of the fader which controls it. The first master selection may then be replaced by a superimposing record and the key thrown, this time in the position opposite to the first, so that the superimposing record is again controlled by the auxiliary potentiometer. The fading operation obviously requires the use of the two superimposing positions of the key.

The invention is not limited to the specific embodiment disclosed herein, but only by the scope of the appended claims.

What is claimed is:

1. In a sound reproducing system, a pair of stylus-operated reproducers, a fader potentiometer, an auxiliary potentiometer, a sound projector circuit, switching means for connecting one of said reproducers to one side of said fader potentiometer, the other of said reproducers to said auxiliary potentiometer and the output circuit of said auxiliary potentiometer to the input of said projector circuit, and switching means for interchanging the reproducers so that the former can be connected to the auxiliary potentiometer and the latter to the fader potentiometer.

2. The combination with a sound reproducing system comprising a pair of electrical sound reproducers, a fader potentiometer connected to the output terminals thereof and a sound projector circuit connected to the output of said fader potentiometer, of an auxiliary potentiometer, switching means for substituting said auxiliary potentiometer for one side of said fader potentiometer, and switching means for connecting the output circuit of said auxiliary potentiometer to said sound projector circuit.

3. The combination in accordance with claim 2 with a resistance element and switching means for including said resistance element in the output circuit of said fader potentiometer simultaneously with the inclusion of the auxiliary potentiometer, the value of said resistance being proportioned to compensate the impedance change in the sound oscillation source due to the inclusion of the auxiliary potentiometer.

4. In a sound reproducing system, a pair of stylus-operated reproducers, a fader potentlometer, an auxiliary potentiometer, a pair of output terminals for connecting with a sound projector circuit and switching means, one end of each of said reproducers being connected together, to the mid-point of said fader potentiometer, to one end of said auxiliary potentiometer and to one of said output terminals, the

other end of one of said reproducers being connectable through said switching means to one end of said fader potentiometer, the other end of the other of said reproducers being connectable through said switching means to the other end of said auxiliary potentiometers and the adjustable contact arm of said auxiliary potentiometer being connectable through said switching means to the adjustable contact arm of said fader potentiometer and to the other output terminal.

5. The combination of claim 4 in which said switching means has three positions, one of which connects one reproducer to one side of said fader potentiometer, the other reproducer to said auxiliary potentiometer and the output circuits of the two potentiometers to said output terminals, the second of which connects the latter reproducer to the other side of said fader" potentiometer, the former reproducer to said auxiliary potentiometer and the output circuits of the two potentiometers to said output terminals, and the third of which removes said auxiliary potentiometer from the circuit, connects each reproducer unit to its respective side of said fader potentiometer and connects the output of said fader potentiometer to said output terminals.

DANIEL C. HICKSON. 

